Vulcanized rubber foamed articles have been widely used for cushioning materials, sealing materials, sound-insulating materials, electrical insulating materials and the like. Recently, vulcanized rubber foamed articles which are more excellent in surface smoothness than the conventional ones have been eagerly desired from the viewpoints of sealing properties and fashionability.
For obtaining vulcanized rubber foamed articles of high surface smoothness, there have been studied various methods such as a method of adjusting a vulcanization speed or a foaming speed and a method of varying a heating means to adjust a heat transfer speed.
Even by utilizing the above methods, however, the obtained vulcanized rubber foamed articles show insufficient surface smoothness, for example, the threshold limit value of the surface roughness thereof is 10 .mu.m when measured using Surfcom 200B (produced by Tokyo Seimitsu Co., Ltd.) according to JIS B-0601.
The present inventors have earnestly studied pursuing vulcanized rubber foamed articles having high surface smoothness, and they have found that the vulcanized rubber foamed articles having high surface smoothness (e.g., those having a surface roughness of less than 10 .mu.m) and having a prominently high shape-retention ratio can be obtained by a process of continuously dipping a vulcanizable and foamable tubular molded product made of a chlorinated ethylene/.alpha.-olefin copolymer rubber, chlorinated polyethylene (CPE) or chlorosulfonated polyethylene which has been extruded from an extruder, in an isopropyl alcohol solution such as an alkylammonium halide solution, and introducing the molded product into a hot air-vulcanizing bath to conduct vulcanization and foaming operation. Thus, the present invention has been accomplished. In recent years, the size of a foamed article used for sealing tends to be made larger and the shape thereof tends to be more complicated. In addition, the foamed article is desired to have a high shape-retention ratio, so that the above-described process for preparing vulcanized rubber foamed articles is very advantageous in industrial use.
The above-described process is also advantageous for preparing vulcanized rubber non-foamed articles having high surface smoothness and high shape-retention ratio.